The present invention relates to methods and apparatus useful as an aid to the diagnosis of arthritic conditions including rheumatoid arthritis, osteoarthritis and gout.
There are numerous (possibly over 100) different types of arthritis of which the three listed above are the most common.
At present, arthritic conditions are diagnosed essentially only when damage to one or more joints has progressed to a sufficiently severe stage that it is diagnosable on the basis of symptoms, but diagnosis may be confirmed by changes visually identifiable on X-ray. For instance, in confirming diagnosis of rheumatoid arthritis affecting the joints of the hand, doctors will look at X-rays of the bones of the hand immediately behind the joint to identify an area of reduced bone density behind the end plate of the bone involved in the joint which shows up as a light spot in the bone on a typical X-ray photograph. However, this feature is only identifiable once the bone density has fallen by about one third of what it would normally be.
Rheumatoid arthritis is often difficult to diagnose because the symptoms usually start gradually and the course of the disease varies from person to person. Physicians diagnose rheumatoid arthritis based on the overall pattern of symptoms, medical history, physical examination and laboratory tests including a blood test. The blood test may help determine if rheumatoid factor is present, an abnormal substance found in the blood of about eighty percent of adults with rheumatoid arthritis. However, the presence or absence of rheumatoid factor does not in itself indicate that the patient has rheumatoid arthritis. Early in the disease, people may notice general fatigue, soreness, stiffness and aching. Pain usually occurs in the same joints on both sides of the body and will usually start in the hands or feet. Rheumatoid arthritis can also affect wrists, elbows, shoulders, neck, knees, hips and ankles. Other symptoms include lumps called rheumatoid nodules under the skin in areas that receive pressure such as the backs of the elbows.
Earlier positive diagnosis of rheumatoid arthritis would assist in studying the disease and in treating its symptoms.
Osteoarthritis or degenerative joint disease is one of the oldest recognised and most common types of arthritis. It is characterised by the breakdown of the joint cartilage causing bone to rub against bone and hence pain and loss of movement. Once again, osteoarthritis is presently diagnosable by only symptoms and at the stage where changes in the joint can be visually identified. However, most people over sixty have osteoarthritis on X-ray but only one third of these have actual symptoms.
Gout is a disease that causes sudden, severe attacks of pain, tenderness, redness, warmth and swelling in some joints. It usually affects one joint at a time. The pain and swelling are caused by uric acid crystals that deposit in a joint. Such attacks may be followed by the development of deforming deposits in the joint.
To allow earlier diagnosis of rheumatoid arthritis and/or differentiation between rheumatoid arthritis and osteoarthritis or gout, and/or monitoring of the progress of a said condition the present invention provides a method for diagnostic imaging comprising producing-one or more images of at least a portion of a bone involved in a potentially arthritic joint based on data reflective of bone density, e.g. an X-ray absorbence image of said bone, said image or images individually or in aggregate including a first region of said bone sufficiently close to said joint to be affected by an arthritic condition and a second region of said bone at least a part of which is spaced from said first region, and providing a read-out of bone density of said first region of said bone relative to the bone density of said second region or of each said bone density separately, and making a comparison of said read-out with at least one value for said read-out indicative of a said arthritic condition, e.g. of rheumatoid arthritis.
The bone densities may each be measured in absolute terms. Alternatively, the values of each region may only be related to the absolute bone density. Preferably, the bone is a bone of the hand, more particularly a finger bone or metacarpal bone, or a bone of the foot, more particularly a toe bone or metatarsal.
Preferably, the second region at least includes a portion spaced from the first region by at least 10 mm, more preferably by at least 20 mm.
The second region is preferably further from the joint than the first region but it is within the scope of the invention for the second region and the first region to be spaced along a line running across the bone so that they are approximately equidistant from the joint.
Preferably, a read out is provided of the bone density along a line axial of said bone extending from said joint.
The region of the bone close to the joint is preferably immediately behind the end plate of the bone. One should ideally measure in an area extending as close to the end of the bone as possible without getting into the soft tissue region or a region where two bones overlap.
Suitably, the read out is of a ratio between the measurements at said first and second regions, e.g. the ratio between a region of local bone density increase immediately adjacent the joint and a bone density found at around the centre of the bone.
However, generally, the bone density (or related value) for the region removed from the joint does not have to be made at the centre of the bone. Any point that may be consistently found in different patients, or on separate occasions in the same patient, may serve. Similarly, the measurement near the joint need not be at the point maximally affected but could be at any reproducible fixed point, e.g. a certain distance from the end plate.
Preferably, one or both of the regions of bone used, preferably both, are ones in which the bone has a high trabecular content. Optionally, both are close to or at the axial centre of the bone.
In an alternative aspect, the invention includes obtaining data relevant to the diagnosis or monitoring of an arthritic condition, comprising measuring the bone density of a portion of a bone involved in a potentially arthritic joint, said portion being adjacent the end of the bone involved in said joint, and comparing said bone density measurement with at least one value for said measurement indicative of a rheumatoid arthritis condition.
The bone density is preferably but not necessarily measured by X-ray absorbence.
For use in either aspect of the invention, there is provided apparatus for use in diagnostic X-ray imaging comprising an X-ray source, means for supporting and fixing in position at least a portion of a hand or foot for imaging using said X-ray source, and a two-dimensional pixel array X-ray detector for producing image data indicative of bone density in said hand or foot or portion thereof. Preferably, the supporting means is adapted to support a finger of the hand or a toe of the foot for imaging and to hold the same still during exposure.